Processing of tobacco is largely an empirical process which includes curing the green tobacco to obtain a cured brown, typically comminuted, preparation which is then aged.
U.S. Pat. No. 4,407,307 to Gaisch et al discloses a form of the process in which cured tobacco is first extracted in the presence of protease for removal of protein and smaller nitrogen-containing substances, the extract subjected to treatment with microorganisms to assimilate proteinaceous and nitrogen-containing compounds, and then, after removing the biomass obtained, resupplying the treated solution to the tobacco so that flavor components not assimilated by the microorganisms are restored to the finished product.
The Gaisch et al process thus approaches the problem of extracting only selected components from the tobacco while permitting the tobacco to retain others by extracting all materials soluble in the presence of enzyme, but permitting microorganisms to effect a useable separation between desirable and undesirable components. Disadvantages of the Gaisch process include the expense required and the relative inefficiency in extracting all nitrogen-containing materials. The present invention offers an improvement in the Gaisch process which partially substitutes treatment with base for treatment with enzyme to achieve a similar end at considerably less cost; by correct adjustment of the conditions, the process is also made more effective. In addition, the present invention provides a more effective alternative to the Gaisch process using a polymerase of plant polymers, such as a carbohydrase in addition to the protease.
As disclosed by Gasich, green tobacco offers no problem with respect to solubility of the protein components, but the extraction is not desirable before curing because the curing process itself is benefited by the presence of what would otherwise be extracted. However, the curing process also evidently converts most of the soluble nitrogen-containing materials of the green leaf to an insoluble form. This insoluble form can, it has now been found, be effectively extracted with dilute base or by the combination of a protease and carbohydrase.